There is disclosed in DE-A-38 11 316, lithotripsy apparatus in which a sealed coupling cushion is filled with water as the coupling medium and is placed on a patient's body so that the shock wave energy can be transmitted through the medium of the water to a concretion to be disintegrated. A gas removal device ensures that the water in the water cushion is gas free and a controlled pressure regulating device ensures that the pressure in the water cushion is at an optimum value. The quality of the water used in the cushion can, however, deteriorate, for example algae may produce slime which reduces the efficiency of the shock wave transmission and thereby impairs the success of the treatment. A defect in the means for circulating the water for the water cushion, may allow water to escape into the open, so as to endanger the sterility of the room in which the patient is being treated. If an open coupling cushion is used the water may escape into the treatment room so that the treatment space or the treatment room must be cleaned and disinfected.
According to the disclosure of DE-A-35 44 628 and DE-A-32 20 751, the ultrasonic shock waves are coupled-in by way of a coupling bag or coupling cushion, filled with gas-free water, which is adapted to the body of the patient with the open part of the coupling bag or cushion contacting the patient or with a membrane shielding the patient. Such an enclosed water circuit has the disadvantage that the growth of algae or the like can cause the coupling medium rapidly to become fouled with slime. DE-A-35 44 628 and DE-A-32 20 751 do not, however, disclose how the water coupling medium is treated in order to prevent slime formation, and in the matter of degasification mention only that air removal tubes can be introduced in the region of the shock wave generator and the sealing edge.
With lithotripsy apparatus of the type under discussion, there is also difficulty in maintaining the contact pressure of the coupling cushion against the body of the patient at an optimum pressure when the weight of the patient's body acts against the coupling cushion. Since during positioning of the patient on the coupling cushion, the coupling medium exerts a counter pressure towards the patient, it may not be possible to bring a stone to be disintegrated into the focus of the shock waves.
EP-A-0 265 741 discloses apparatus for destroying concretions in the body of a living being. The apparatus comprises disintegrating shock wave generators, filled with a liquid coupling medium, and a liquid circuit with a container and circulating pump. The circulation of the liquid is in an operating circuit and a filling and gas removal circuit. In the filling and gas removal circuit, gas is removed from the liquid supplied with the aid of a vacuum pump and is subsequently fed from a storage container to the shock wave generator or generators.
This apparatus has the disadvantage that the use of containers for preparing the liquid and for removing gas from the liquid, entails that the apparatus is uneconomical of space. Further, since the coupling medium becomes fouled with slime it must be constantly replaced after only short periods of time.
Apart from the disadvantages just mentioned, particular care must be taken to ensure that no germs are transferred from patient to patient by way of the coupling medium, especially if the coupling cushion is exposed towards the patient.